The present invention relates to drilling and blasting in general and, more particularly, to an expeditious method for excavating a tunnel without the need for cleaning lifter holes.
Hard rock mining, tunneling and shaft sinking are difficult and expensive endeavors fraught with skill, safety and time considerations.
Considerable effort has been expended in improving the efficiency of tunneling operations. Over the years, new and improved techniques, equipment and blasting regimens have been proposed and implemented to increase underground safety and productivity. Yet the fact remains that hard rock excavating is a tough undertaking. Every bit of the hard earned progress inures to the benefit of industry, society and personnel.
When an improved drilling and blasting technique is used for excavation, a reduction in cycle time increases advance rates, safety and improves overall economic benefits.
One area of concern is the reduction of cycling times. By eliminating activities that consume or occupy but not directly contribute to the advance of tunnel face, additional efficiencies maybe realized.
Using present drilling and blasting techniques, operators must manually locate, dig out and clean lifter holes. Lifter holes (also known as blast holes) are drilled holes oriented along the floor of a tunnel in the direction of the advance and are required to ensure the grade or slope of the tunnel meets design specifications. Explosives are loaded into the lifter holes.
During tunnel driving prior to the insertion of explosives, the lifter holes get filled with mud, cuttings, debris, etc., and become buried. The entire heading must be then manually shoveled out to gain access to the holes. The lifter holes must be literally dug out and cleaned by handxe2x80x94a long laborious process.
In order to eliminate or reduce the time and money wasting paradigm of cleaning or mucking lifter holes, a research project was initiated with the objective to perfect a technique that would ensure a drift floor could be reliably excavated without the need to dig out, clean and load lifter holes.
U.S. Pat. No. 5,232,268 to Dergler et al., suggests a method for tunneling by drilling a large diametered central relief hole surrounded by a series of smaller diameter concentric substantially axially parallel primary and secondary blast holes. Explosives are placed in the relief hole and in most, if not all, of the primary and secondary holes. The central relief hole is drilled deeper than the other holes. The inventors state that by using their methodology, the difficult prior practice of drilling exactly parallel holes is replaced by approximately axially parallel relief holes.
U.S. Pat. No. 4,611,856 to Cha et al., teaches the use of parallel blast holes. Although shale oil recovery is markedly different than hard rock mining, the patent demonstrates the use of xe2x80x9cparallel rows of holes extending across the horizontal cross-section of the retort sitexe2x80x9d Col. 6, line 26. Angled drill holes at the base of the retort permit the formation of the tapered lower portion of the retort.
The aforementioned references provide examples of prior art parallel drilling techniques. There is no recognition of the hard rock problems encountered with lifter holes.
There is provided a technique for excavating hard rock stopes, drifts, tunnels, shafts and the like by drilling an array of closely spaced concentrated line drill holes at the base of the rock face. These line drill holes may be slightly angled with respect to the blast holes. Not loaded with explosives, these line drill holes are xe2x80x9cexpendablexe2x80x9d and act as crack indications where compression waves generated from the nearest blast hole are reflected and concentrated as tensile waves used to fail the rock between a predetermined plane and a blast hole.